Studies on bovine besnoitiosis with special reference to the aetiology

Abstract

(1) A brief historical review of bovine besnoitiosis is given. (2) The importance of the disease as a veterinary and economic problem is stressed. (3) The identification of the causal agent, Besnoitia besnoiti (Marotel, 1913), has made it possible to give a concise definition of the disease. (4) The synonyms of bovine besnoitiosis are listed. (5) The distribution of bovine and equine besnoitiosis in Europe and Africa, and the occurrence of murine besnoitiosis in the United States of America are recorded. (6) A detailed account of the aetiology, based on observations made on rabbits and cattle, is offered. (7) Systematic studies on the development of the parasite cyst revealed that the cyst wall is of somatic origin. (8) The inner and intermediate membranes of the wall are derived from the markedly hypertrophied polynucleated host cell, the histiocyte, while the outer wall is formed by collagenous fibres. (9) The term pseudocyst, as applied by Jacobs (1956) for the Toxoplasma cyst where the cyst wall is also of somatic origin, should be used in the same sense for the Besnoitia cyst. (10) Certain chemical components of the parasite and cystic wall have been determined by histochemical tissue reactions. (11) Asexual reproduction by longitudinal binary fission within either monocytes or histiocytes is the only form of multiplication in the vertebrate host. (12) The "Fuls" B. besnoiti strain has been maintained by serial passage in rabbits for 125 generations. A gradual decrease in virulence of the parasite was noticed as the passage level increased. (13) B. besnoiti remains viable in citrated blood for 48 hours at 20°C, and for 96 hours at + 4° C. (14) A detailed survey of the complicated history of the nomenclature of certain Protozoa included in the genera Balbiania, Besnoitia, Eimeria, Fibrocystis, Gastrocystis, Globidium, Haplogastrocystis, Ileocystis, Lymphocystis, Sarcocystis and Toxoplasma is given. (15) Evidence has been brought forward that Besnoitia is a valid genus, that it is related to the genera Fibrocystis and Toxoplasma, but distinct from any of the remaining genera. (J 6) Absence of any characteristic features does not permit placing the genera Toxoplasma, Besnoitia and Fibrocystis in any natural scheme of classification in the Protozoa, and hence it is proposed to group them as "Parasites of Doubtful Nature". (17) It has been determined that, besides cattle and rabbits, sheep, goats and guinea pigs are susceptible, while two horses, a dog and several mice, rats, fowls and dassies failed to develop a microscopic infection and clinical symptoms after artificial infection. (18) The pathogenesis is discussed. (19) The natural mode of transmission is obscure. (20) Information on the epizootology is limited. (21) The symptomatology of bovine besnoitiosis in cattle, sheep, goats, rabbits and guinea pigs is described. (22) Bulls that survive a natural infection develop either a temporary or permanent sterility. (23) A temporary sterility, as determined by systematic microscopic semen examination of artificially infected animals, persisted for approximately six months in two bulls, for about three months in a billy goat, and four months in a ram. (24) Methods for making a diagnosis are described. In inapparent or atypical infections in male ruminants, aspermatogenesis can be used as a guide for making a diagnosis. (25) Investigations on bovine besnoitiosis have not advanced far enough to evolve reliable prophylactic measures. (26) Animals that survive either a natural or an artificial infection develop a durable premunity. (27) Photographs showing the course of the disease in a bull, the pronounced sclerodermatitis in a chronically affected animal, the development of a parasitic cyst in a bull and a rabbit, and the morphology and method of reproduction of B. besnoiti are presented.